1. Field of the Invention
The present invention relates to marine vessel hulls utilizing pressurized gas cushions maintained in a recess in a portion of the bottom of the hull for reduction of water drag on the hull, thereby increasing the speed and fuel efficiency of the vessel. This invention more particularly relates to a marine vessel having a catamaran configuration with each catamaran side hull having a pressurized gas cushion.
2. Description of the Prior Art
One of the primary objectives in boat design is to reduce the amount of drag caused by the interface of the hull with the water surface. Early planing hulls were designed so that forward motion of the hull raised the vessel to cause it to ride on a smaller portion of its hull surface resulting in reduced hull-to-water friction. The design of hydrofoil vessels further reduced hull contact with the water by attaching foils to the hulls upon which the boats ride at high speed. Some marine vessels interpose a film of air between the vessel's hull and the water to reduce the hull-to-water friction. One example is illustrated in U.S. Pat. No. 3,191,572 issued to H. A. Wilson in which a tri-hulled vessel has air introduced along the bottom of each hull. This air is allowed to stream freely from the stern of the vessel. U.S. Pat. No. 4,031,841 issued to Bredt also discloses the technology for an air film hull. The Bredt and Wilson hulls still ride with the hull relatively low in the water so that much of the sides of the hulls maintain contact with the water, but the drag between a portion of the bottom is somewhat reduced by a film of air mixed with water.
Surface effect ships were an improvement over the air film hulls as the hulls of surface effect ships are raised out of the water by a pressurized air cushion that is partially captured within the hull of the vessel. The prior art of air cushion vessel hull designs have contained the air cushion with flexible seals, which are a rubberized curtain, either all around the vessel as in the case of the hovercraft air cushioned vessels, or across the front and the back of the vessel with thin parallel side hulls that provide a side seal for the air cushion as in the case of surface effect ships. The flexible seals reduce the amount of air lost from the air cushion but create a rough ride, "a cobble stone ride," even in smooth water. As the surface of the water becomes rougher the flexible seals can be separated from each other, causing further deterioration in ride quality. Also, in rough water the flexible seals frequently fail to maintain the air cushion, causing the craft's hull to drop lower into the water until the seal is regained and the air cushion is reestablished. The loss of the air cushion increases the hull contact with the water increasing the hull-to-water friction and significantly slowing the vessel. Seals are a high maintenance problem with frequent breakage that results in permanent loss of air cushion and a slow ride to the repair yard. Such surface effect ships are disclosed by U.S. Pat. Nos. 5,415,120, and 4,392,445 issued to Donald E. Burg and U.S. Pat. No. 4,523,536 issued to Mark H. Smoot.
Notwithstanding the existence of such prior art for surface effect ships, it remains clear that there is a need for a vessel which will maintain a relatively smooth ride and maintain the air cushion whether the water is smooth or rough without the use of flexible seals. Also, there is a need to improve the stability of surface effect ships which are notoriously unstable in rough water.